Serial attached SCSI (SAS) is a communication protocol which mainly used to standardize data access of a computer storage device (such as a hard disk or a tape drive, etc.). SAS is a point-to-point serial protocol for replacing the parallel SCSI bus technology promoted in the mid 1980's. The SAS device uses differential signals to allow communication. The differential signals can reduce negative effects, such as capacity effect, inductance effect, noise and so on, which the parallel SCSI suffers under high-speed communication transmission, and achieves a stable and high-speed serial communication.
The SAS succeeds to the frame formats and full-duplex communication of the standard 15 SCSI command set and the fiber channel protocol. Each SAS device includes at least a transceiver mechanism, which includes a transmitter and a receiver. Two pair of conductive wires can be used to connect the transmitters and corresponding receivers in connecting ports of two devices. Under the full-duplex communication, each transceiver mechanism can transmit and receive data via the two pairs of conductive wires.
The connecting ports of the two devices can be connected to a connector via connecting wires. Two pairs of conducting wires may be connected to two pairs of terminals on the connector, respectively. The physical link rate of the first-generation SAS is 3.0 Gbps (Gbit/s), and the second-generation SAS, whose physical link rate is twice as much as the first-generation SAS and up to 6.0 Gbps, is the main trend currently. In the near future, the third-generation SAS may be promoted, and its physical link rate will further increase to be twice as much as the second-generation SAS and up to 12 Gbps. Since the arrangement of the terminal pins of the third-generation SAS is the same as that of the second-generation SAS, when the physical link rate increases to 12 Gbps, some problems that the current connectors may have is electromagnetic interference (EMI emission), the two pairs of terminals may have cross-talking, and so on, may be faced.